FERTILIZATION AFTER INITIATION OF DEVELOPMENT. 259 



The egg of the sea-urchin cannot be fertilized before maturation 

 has taken place, even though the spermatozoon may enter the 

 egg. Penetration is not fertilization. However, if a spermato- 

 zoon enters immediately after maturation, normal changes 

 characteristic of fertilization are produced. But shortly after 

 the act of fertilization the egg returns again to a condition in 

 which fertilization is impossible. E. B. Wilson 1 has demon- 

 strated for Cerebratulus that if pieces of fertilized eggs are dropped 

 into sea-water containing active spermatozoa there is no reaction 

 between the pieces of eggs and sperm; however, with pieces of 

 unfertilized eggs there is a reaction. Delage, too, has noted 

 that starfish eggs which had been exposed to artificial partheno- 

 genetic agents could not be fertilized. 2 



Maturation, then, leads to changes within the egg that make 

 possible initiation of development by either a spermatozoon or 

 an artificial stimulus. And if this initiation of development is 

 brought about, carrying with it of course a change of the egg 

 system, fertilization is thereby rendered impossible. 



It would seem strange not to suppose that an egg ' passes 

 through essentially similar physiological changes during the 

 development from one cell to a swimming pluteus, whether 

 activation has been produced artificially or by a spermatozoon. 

 If activation by a spermatozoon produces a physiological state 

 of reactivity that leads to development, and, if activation by 

 artificial agents also produces physiological changes that lead 

 to the same kind of development, should we not suppose that 

 the egg the only common factor would pass through essen- 

 tially similar conditions in the two cases? One would judge from 

 the papers of Loeb, that this supposition is erroneous, that " 

 sperm will react with artificially activated eggs in an entirely 

 normal manner, producing normal swimming larvae, while it is 

 positively known that such is not the case when activation has 

 been previously affected by means of a spermatozoon. 



The writer has presented proof that eggs of the sea-urchin 

 activated by butyric acid, and resulting in the production of 

 normal membranes, will not react with sperm nor become fer- 



1 Wilson, '03. 



2 Delage, '01. 



